In the production of communication systems such as radios and in the production of vehicles which includes the installation of radios, it is well known to test the communication apparatus before delivery to the customer. In view of the numerous components employed in such systems, and the distribution of such components throughout a vehicle in which it is installed, a point-by-point inspection of all the connections between components in the system is very difficult if not impossible. Moreover, it may be appreciated that visual inspection may not readily identify electrical connection problems which can render the system inoperative or raise the risk of damage to those components improperly connected. Accordingly, diagnostic devices have been developed in order to test the operation of the communication systems.
One previously known form of apparatus for testing communication systems involves a separate apparatus which is adapted to interact with various portions of the system. For example, radio tuners, amplifiers, demodulators and the like may be tested by interacting with the circuitry in the testing apparatus. Likewise, the testing circuitry may emit signals which are transferred to other portions of the system to determine the functioning of certain-controls or circuits such as the tone controls, speakers or a graphic equalizer. However, such systems require connection of the testing apparatus with portions of the radio being tested and must be accomplished by disconnecting portions of the system for reconnection to the test apparatus. As a result, the preparation for testing of the radio system with these previously known test apparatus can be laborious, difficult and time consuming to perform.
It has also been known to provide the communication apparatus with self-testing circuitry. However, such circuitry, particularly circuits designed for use in an analysis of analog signals, can be quite complicated, and may substantially increase the size and expense of producing the communication apparatus. Moreover, such apparatus is often limited to testing of discreet signal functions, and does not permit variation of a single signal parameter through a range in which the communication device should operate properly. In particular, such variation may have to be performed manually and thus requires experience and expertise in order to operate the testing equipment properly.
In addition, while parts of the communication system, for example, the radio tuner, may be inspected at the factory for operation before installation in the vehicle, it is necessary to determine that the communication system is functional once it has been installed in the vehicle. Nevertheless, the previously known test apparatus do not permit detection of whether the entire system has been properly installed in a vehicle or other environment. In particular, the installation of a system often requires widely distributed speakers to be connected to the amplifier. In light of recent improvements in audio reproduction systems, where concert hall emulation and other features have been made available by digital signal processing, the operation of each speaker within the system has greater importance than in previously known mono or stereo systems since each speaker has a distinct contribution to the audio output and is not merely a redundant audio source. Accordingly, the connection between each speaker and an amplifier is very important to system operation but is very difficult to monitor within the assembled vehicle.